The present disclosure relates to measuring while drilling techniques and, more particularly, to systems and methods for automatic weight on bit sensor calibration and regulating buckling of a drillstring.
To obtain hydrocarbons such as oil and gas, boreholes are drilled by rotating a drill bit attached at a drillstring end. A large proportion of the current drilling activity involves directional drilling; i.e., drilling deviated and/or horizontal boreholes, to increase the hydrocarbon production from subterranean formations. Modern directional drilling systems generally employ a drillstring having a bottom-hole assembly (BHA) and a drill bit situated at an end thereof that may be rotated by rotating the drillstring from the surface, using a mud motor (i.e., downhole motor) arranged downhole near the drill bit, or a combination of the mud motor and rotation of the drillstring from the surface. Pressurized drilling fluid, commonly referred to as “mud” or “drilling mud,” is pumped into the drill pipe to cool the drill bit and flush cuttings and particulates back to the surface for processing. The mud may also be used to rotate the mud motor and thereby rotate the drill bit.
The BHA generally includes a number of downhole devices placed in close proximity to the drill bit and configured to measure certain downhole operating parameters associated with the drillstring and drill bit. Such devices typically include sensors for measuring downhole temperature and pressure, azimuth and inclination measuring devices, and a resistivity measuring device to determine the presence of hydrocarbons and water. Additional downhole instruments, known as logging-while-drilling (“LWD”) and measuring-while-drilling (“MWD”) tools, are frequently attached to the drillstring to determine the formation geology and formation fluid conditions during the drilling operations.
Boreholes are usually drilled along predetermined paths and the drilling of a typical borehole proceeds through various formations. To optimize drilling operations, a drilling operator at the surface controls the surface-controlled drilling parameters, such as weight on bit, drilling fluid flow through the drill pipe, the drillstring rotational speed, and the density and viscosity of the drilling fluid. The downhole operating conditions continually change and the drilling operator must be able to react to such changes and adjust the surface-controlled parameters to optimize the drilling operations.
During drilling operations, gravity and hole curvature directly impact drilling performance as related to accurately determining the true weight that is applied on the drill bit. Without knowing the masking effects created by gravity and hole curvature it can become extremely difficult to determine whether weight is being applied to the bottom of the hole correctly. At least one problem encountered is not knowing the true hole curvature, inclination, and azimuth until after a survey probe attached to the BHA measures the hole inclination and azimuth at a new depth. Until the survey probe reaches that depth, there is a depth lag in data in knowing just exactly what the hole curvature is from the point of the survey measurement to the bottom of the hole. Currently, it is believed that there is no way of knowing what the true hole curvature, azimuth, and inclination is below the survey probe or instrument.